The present invention relates to an adhesive, an adhesive member, an interconnecting substrate for semiconductor mounting having the adhesive member, and a semiconductor device comprising a semiconductor chip and an interconnecting substrate bonded together by using the adhesive member.
With the progress of electronic and electric equipment in recent years, the mounting density of electronic parts has been increased, and new packaging methods have becoming to be used, such as so-called chip scale packages or chip size packages (hereinafter, they will be referred to as CSP) with sizes nearly equal to semiconductor chips, and bare chip packaging.
Reliability is one of the most important characteristics requisite for packaging substrates mounted with various electronic parts, such as semiconductor elements. Particularly, connection reliability against thermal fatigue is very important because it directly affects the equipment containing the packaging substrates.
One of the causes for the lowering of connection reliability is the thermal stress due to the use of various materials having different coefficients of thermal expansion. That is, semiconductor chips have coefficients of thermal expansion of as small as about 4 ppm/xc2x0 C. while wiring boards for mounting electronic parts have coefficients of thermal expansion of as large as 15 ppm/xc2x0 C. or more, so that thermal shock results in thermal strain, which results in a thermal stress.
In conventional substrates mounted with semiconductor packages containing lead frames, such as QFP or SOP, the deformation of lead frames absorbs the thermal stress to keep reliability.
In bare chip packaging wherein the electrodes of semiconductor chips and the wiring pads of wiring boards are connected by solder balls or by a conductive paste through small projections referred to as bumps, thermal stress concentrates to the connecting regions, to lower connecting reliability. Putting a resin referred to as xe2x80x9cunder fillxe2x80x9d between chips and wiring boards is known to effectively disperse the thermal stress, but increases packaging steps and cost. Another method is connecting the electrodes of semiconductor chips and the wiring pads of wiring boards by conventional wire bonding, which, however, also increases the packaging steps because wires should be protected by coating a sealing resin.
Because CSP can be mounted together with other electronic parts, various structures have been proposed as disclosed in Surface Mounting Technique, 1997-3, xe2x80x9cThe future of CSP (fine pitch BGA) being put into practical usexe2x80x9d, p 5, Table 1, published by Nikkan Kogyo Shinbunsha. Among them, those containing a tape or carrier substrate as an interconnecting substrate called xe2x80x9cinterposerxe2x80x9d have been increasingly put into practical use. In the above-described table, the structures developed by Tecera Co., Ltd. and TI Co., Ltd. correspond to the above-described structures. Because they contain an interconnecting substrate as an interposer, they excel in connection reliability as published in Shingaku Giho CPM96-121, ICD96-160 (1996-12), xe2x80x9cDevelopment of Tape/BGA-type CSPxe2x80x9d and Sharp Giho, No. 66 (1996-12), xe2x80x9cChip Size Package Developmentxe2x80x9d.
Between the semiconductor chip and the interconnecting substrate called interposer contained in such a CSP is used an adhesive member that decreases the thermal stress resulting from their difference in coefficient of thermal expansion. The adhesive member requires moisture resistance and high temperature endurance, and there is a demand for film-form adhesive members, which facilitate the production process control.
Adhesives of the film type have been used in flexible printed wiring-boards, and most of them contain acrylonitrile butadiene rubber as a main component.
Among those for printed wiring boards that are improved in moisture resistance include an adhesive disclosed in Japanese Patent Application Unexamined Publication No. 60-243180 (1985) which contains an acrylic resin, an epoxy resin a polyisocyanate and an inorganic filler, and an adhesive disclosed in Japanese Patent Application Unexamined Publication No. 61-138680 (1986) which contains an acrylic resin, an epoxy resin, a compound having urethane bonds in molecules and terminated by a primary amine at each end and an inorganic filler.
The adhesive members as described above should release thermal stress and be heat and moisture resistant. In view of production processes, they also should neither allow an adhesive to flow out to electrode areas provided on semiconductor chips for electric signal output nor leave vacant spaces between them and circuits formed on interconnecting substrates. Flowing out of an adhesive to electrode areas causes connection defects of electrodes, and vacant spaces between a circuit and an adhesive tend to deteriorate heat resistance and moisture resistance. It is therefore important to control the flowing amount of adhesives. Further, film-form adhesives containing thermosetting resins are subject to change with passage of time, thereby decreasing the flowing amount and bonding strength. Adhesive members, therefore, require control of the flowing amount and bonding strength throughout their usable periods.
Film-form adhesives containing thermosetting resins gradually cure during storage. The adhesives further cure during various processes for producing a package, including mounting a semiconductor chip on an interconnecting substrate called interposer, fabrication of a package, etc. It is preferable to use an adhesive having a longer usable period to improve the processability of the adhesive and the connection reliability of semiconductor chips. That is, the longer the usable period is, the less the flowing amount and bonding strength decrease due to the change with passage of time, facilitating the control of the flowing amount and bonding strength.
The usable periods of conventional film-form adhesives could be increased by decreasing the content of the curing accelerator in an adhesive composition, but the curing rate was problematically lowered on curing the adhesives to cause foaming. There has been a demand for adhesives, which do not foam but have longer usable periods and as well satisfy the requirement for low elasticity, heat resistance and moisture resistance.
Further, adhesives for use in semiconductor packages or wiring generally contain thermosetting high molecular weight components such as epoxy resins to improve heat resistance. The thermosetting high molecular weight components, however, have the defects of requiring a high temperature and a long time for curing. To solve the defect, curing accelerators have been used together with the thermosetting resins. Blending a curing accelerator greatly improves the curability, but has caused another problem that the reaction proceeds even at room temperature, thereby changing the flowability of the adhesive during storage at room temperature to make the adhesive commercially useless. To solve the new problem, it was proposed to use a latent curing accelerator having no activity at room temperature. For example, Japanese Patent Application Unexamined Publication No. 9-302313 (1997) discloses the use of a very latent imidazole as a curing accelerator for epoxy resins in adhesive compositions. The latent curing accelerator improves storage stability. However, it has been found that because the production process of adhesive films includes a heat treatment step for curing the adhesive composition to B-stage and the partially reacted latent curing accelerator becomes active even at room temperature, the reaction gradually proceeds to deteriorate storage stability. This has caused a demand for further improvement of storage stability.
An object of the invention is to provide an adhesive and an adhesive member, which have a usable period of 3 months or more at 25xc2x0 C. without deteriorating the low elasticity, heat resistance and moisture resistance necessary for mounting a semiconductor chip onto an interconnecting substrate, referred to as interposer, such as a glass-epoxy substrate or a flexible substrate, which are a largely different in coefficient of thermal expansion. Other objects of the invention is to provide an interconnecting substrate for semiconductor mounting having the adhesive member and to provide a semiconductor device wherein a semiconductor chip and an interconnecting substrate are bonded together by using the adhesive member.
Further, during the production of adhesive films, curing accelerators partially undergo reaction in the step of heat treatment at high temperatures in a coating drying furnace, so that the curing accelerators exhibit activity due to decomposition, etc., even during storage at room temperature, not excepting latent curing accelerators. It has been found that the crosslinking polymer component in the films is crosslinked due to its particularly high activity, thereby changing flowability largely and deteriorating storage stability. In view of this problem, another object of the invention is to provide an adhesive to be used for producing adhesive films particularly excelling in storage stability.
Accordingly, the present invention relates to the followings.
1) An adhesive (hereinafter, it may be referred to as adhesive A), comprising (1) 100 parts by weight of an epoxy resin and a hardener therefor, (2) 75 to 300 parts by weight of an epoxidized acrylic copolymer having a glycidyl (meth)acrylate unit content of 0.5 to 6 wt. %, a glass transition temperature Tg of xe2x88x9210xc2x0 C. or higher and a weight average molecular weight of 100,000 or more and (3) 0.1 to 20 parts by weight of a latent curing accelerator.
2) An adhesive, comprising (1) 100 parts by weight of an epoxy resin and a hardener therefor, (2) 5 to 40 parts by weight of a high molecular weight resin being compatible with the epoxy resin and having a weight average molecular weight of 30,000 or more, (3) 75 to 300 parts by weight of an epoxidized acrylic copolymer having a glycidyl (meth)acrylate unit content of 0.5 to 6 wt. %, a glass transition temperature Tg of xe2x88x9210xc2x0 C. or higher and a weight average molecular weight of 100,000 or more and (4) 0.1 to 20 parts by weight of a latent curing accelerator.
3) The adhesive of 1) or 2), wherein the latent curing accelerator is an adduct curing accelerator.
4) The adhesive of 3), wherein the latent curing accelerator is an amine adduct.
5) The adhesive of 4), wherein the latent curing accelerator is an amine-epoxy adduct.
6) The adhesive of any one of 1) to 5), which contains 1 to 20 parts by volume of an inorganic filler relative to 100 parts by volume of a resin content of the adhesive.
7) The adhesive of 6), wherein the inorganic filler is alumina, silica, aluminum hydroxide or antimony oxide.
8) The adhesive of any one of 1) to 7), which has generated 10 to 40% of heat to be generated by complete curing thereof as measured by DSC.
9) The adhesive of any one of 1) to 8), which has a residual solvent content of 5 wt. % or less.
10) The adhesive of any one of 1) to 9), which gives a cured product thereof having a storage modulus of 20 to 2,000 MPa at 25xc2x0 C. and having a storage modulus of 3 to 50 MPa at 260xc2x0 C. as measured by using a dynamic viscoelasticity measuring apparatus.
11) An adhesive (hereinafter, it may be referred to as adhesive B), which is an adhesive composition comprising two kinds of resins which when the composition is in a B-stage state, separate from each other into a disperse phase and a continuous phase, a hardener and a curing accelerator, wherein in the B-stage state, the curing accelerator is compatible with the disperse phase and separates from the continuous phase.
12) The adhesive of 11), wherein in the B-stage state, the disperse phase contains an epoxy resin and the curing agent as main components, and the continuous phase contains as a main component a high molecular weight component having a weight average molecular weight of 100,000 or more.
13) The adhesive of 12), wherein the high molecular weight component having a weight average molecular weight of 100,000 or more is an epoxidized acrylic copolymer having a glycidyl methacrylate unit content or a glycidyl acrylate unit content of 2 to 6 wt. %.
14) The adhesive of any one of 11) to 13), wherein the curing accelerator is an amine-epoxy adduct.
15) An adhesive member of a film form, comprising a carrier film and a layer of the adhesive of any one of 1) to 14) formed on the carrier film.
16) An adhesive member, comprising a core material and a layer of the adhesive of any one of 1) to 14) formed on each side of the core material.
17) The adhesive member of 16), wherein the core member is a heat resistant thermoplastic film.
18) The adhesive member of 17), wherein the heat resistant thermoplastic film has a softening temperature of 260xc2x0 C. or higher.
19) The adhesive member of 17) or 18), wherein the core material or the heat resistant thermoplastic film is a porous film.
20) The adhesive member of any one of 17) to 19), wherein the heat resistant thermoplastic film is a liquid crystalline polymer.
21) The adhesive member of any one of 17) to 20), wherein the heat resistant thermoplastic film is a polyamideimide, a polyimide, a polyetherimide or a polyether sulfone.
22) The adhesive member of any one of 17) to 20), wherein the heat resistant thermoplastic film is a polytetrafluoroethylene, an ethylene-tetrafluoroethylene copolymer, a tetrafluoroethylene-hexafluoropropylene copolymer or a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer.
23) An interconnecting substrate for semiconductor mounting, comprising
an interconnecting substrate having a semiconductor chip mounting surface and
the adhesive member of any one of 15) to 22) stuck on the semiconductor chip-mounting surface of the interconnecting substrate.
24) A semiconductor device, comprising a semiconductor chip and an interconnecting substrate bonded together by using the adhesive member of any one of 15) to 22).
25) A semiconductor device, comprising an interconnecting substrate and a semiconductor chip having an area of 70% or more of an area of the interconnecting substrate, the interconnecting substrate and the semiconductor chip being bonded together by using the adhesive member of any one of 15) to 22).